1. Field of the Invention:
This invention relates to the art of dissolved air flotation clarifiers and specifically relates to travelling bridge clarifiers operating on a combined dissolved air flotation and sludge settling process.
2. Prior Art:
Travelling bridge clarifiers or settling tanks are disclosed and claimed in our U.S. Pat. No. 4,193,871 issued Mar. 18, 1980. In these clarifiers heavy sludge settles to the bottom of the tank and is removed by suction heads suspended from the travelling bridge while lighter sludge floats to the top of the pond in the tank and is skimmed into a collector trough near the discharge end of the tank.
Dissolved air flotation systems for separating grease or fine particulate matter from industrial waste liquids are also known in the art but these systems require a constant horizontal velocity in the direction of flow of the liquid through a flotation tank which is slow enough to allow clarified liquid to form at the bottom of the tank and flow to the tank outlet without entraining air bubbles in the effluent.
It would be an improvement in the art to combine dissolved air flotation and heavy sludge settlement clarification of waste liquid in a single tank thereby speeding up the clarification process and increasing the capacity of travelling bridge clarifiers so that they may be made small enough to be easily portable for transfer to the sites of industrial equipment containing liquids to be clarified.
It would be a further improvement in the art to increase the saturation of air in the liquid introduced into the tank to effect the flotation and to remove the clarified liquid as soon as it is formed at levels adjacent the top of the tank.